1. Field of the Invention
The invention relates to a navigation apparatus and, more particularly, a navigation apparatus employing real image data that correspond to images such as a satellite photograph depicting the surface of the earth and an aerial photograph.
2. Description of the Related Art
In the related art, a navigation apparatus displays a map on a screen of a display device based on road map data recorded in the DVD-ROM, etc., displays own location on the map based on own location data, and guides a user onto routes to a destination.
However, in the navigation apparatus in the related art, the map screen to be displayed is formed by using map data. Therefore, there is such a problem that it is difficult to understand own current location and grasp the actual situation around own current location through the map screen.
This is because it is difficult to display the vertical positional relationship such as roads in a solid crossing, on the map screen and because actually a large number of roads, buildings, and the like that are not displayed on the map screen a re present.
As one of solutions for overcoming such problem, JP-A-Hei.5-113343 discloses that own current location is displayed on an aerial photograph screen that is prepared from aerial photograph data. If such aerial photograph screen is employed, the building or the like serving as a mark can be very easily understood. Thus, there are such advantages that own current location can be easily understood and also the actual situation around own current location can be easily grasped.
However, the aerial photograph screen (prepared by using the aerial photograph data) does not in all cases make it possible to understand own current location more easily and grasp the situation around own current location more easily in contrast to the map screen (prepared by using the map data). Rather, in some cases own current location can be easily understood using the map screen rather than the aerial photograph screen.
Also, the aerial photograph data employed to prepare the real image such as the aerial photograph screen need a large quantity of data. Thus, if the aerial photograph data are stored in the memory device, the compression process must be applied. Therefore, if the aerial photograph data are employed, the original aerial photograph data must be obtained by applying the restoration (depression, expansion) process to the aerial photograph data, which have been subjected to the compression process, to display the real image.
The restoration process is not carried out in an instant. For example, it takes almost several seconds to display a sheet of the aerial photograph screen on the screen of the display device. Therefore, there is such a problem that, unlike the map screen in the related art, the screen cannot be continuously updated so as to respond to the moving of own location.
In this manner, the aerial photograph screen is not superior in all respects to the map screen. As a result, it is supposed that not a navigation apparatus utilizing the aerial photograph screen only (of course, a navigation apparatus utilizing the conventional map screen only) but a navigation apparatus system utilizing both the aerial photograph screen and the map screen becomes the mainstream in the next generation.
Accordingly, in the future, it becomes important to use properly the real image such as the aerial photograph screen and the map screen, which have above two different features.